Technical Field
The present invention relates to photovoltaic devices, and more particularly to methods and devices where atomic layer deposition processes are employed to provide buffer layers and/or passivation layers for a Cu—Zn—Sn containing chalcogenide compound absorber layer.
Description of the Related Art
A solar cell may be described in terms of a fill factor (FF). FF is a ratio of the maximum power point (Pm) divided by open circuit voltage (Voc) and short circuit current (Jsc):
  FF  =                    P        m                              V          oc                ⁢                  J          sc                      .  The fill factor is directly affected by the values of a cell's series and shunt resistance. Increasing the shunt resistance (Rsh) and decreasing the series resistance (Rs) will lead to a higher fill factor, thus resulting in greater efficiency, and pushing the cells output power closer towards its theoretical maximum. The increased efficiency of photovoltaic devices is of utmost importance in the current energy environment.
Emitter-absorber photovoltaic devices often include exotic materials that are both rare and often toxic. For example, thin-film materials of the type Cu(In,Ga)(S,Se)2 (CIGS), while efficient, include rare indium metal, which is expected to be of high cost and short supply in future large-scale photovoltaic device production—an issue which is further exacerbated by the growing indium consumption for thin film display production. Other materials such as Cu2S and CdTe have also been proposed as absorbers but while Cu2S suffers from low stability in devices, rare tellurium and toxic cadmium limits CdTe usage.